Connecting Media

 

There are three general classes of media types: coaxial cable, twisted pair and fiber optic cable. Coaxial cable had suffered waning popularity, but is making a bit of a comeback with cable modem solutions. There are two types of fiber-optic cable: multi mode fiber and single mode fiber. Twisted pair is the most common type of computer network cabling. Twisted pair can be classified according to the value of the intrinsic impedance of the wire, and whether it is shielded or unshielded. Unshielded twisted pair, with an intrinsic impedance of 100 ohms, is the most common type of computer network cabling used today.

Coaxial Cable

A coaxial cable has a central conductor.

Coaxial cable uses a single conductor in the middle of a cable. The central conductor is surrounded by an insulator called the dielectric. A conductive shield is put around the dielectric. This shield acts as the second conductor for the circuit as well serves to protect the inner conductor from interference. Coaxial cable for local area network (LAN) connections is obsolete. Coaxial cable is being used in some cases for delivering the last mile of service. For e.g., coaxial cables are being used by Cable TV networks to deliver high-speed service customer premises.

Unshielded Twisted Pair

UTP cable is the most common.

Unshielded twisted pair cabling, or UTP cabling, is the most common type of network cabling. It consists of four twisted pairs of wire, each with a different number of twists per foot, all encased on one sheath. UTP cabling is graded according to category. Category 3 and 4 were replaced by Category 5 cabling by the year 2000. Category 5 is recommended for running Ethernet at speeds of 100 Mbps. Category 5e, was introduced to run gigabit Ethernet or 1000BaseT networks. Category 6 and Category 6a have since been introduced to give better performance at higher speeds. UTP cabling has an intrinsic impedance of 100 ohms.

Shielded Twisted Pair

FTP or ScTP has a metal back to ground the shield.

There are two types of shielded twisted pair wiring. In the 1980s and 1990s shielded twisted pair was promoted as the best wire type for Token Ring networks. This had an intrinsic impedance of 150 ohms. A new wiring trend is to use 100 ohm shielded twisted pair. The shielding reduces noise and increases the performance of the cable. These are sometimes called foiled twisted pair, or FTP (not to be confused with file transfer protocol) or sometimes called screened twisted pair, or ScTP. These types of cables are compatible with normal UTP.

Multi Mode Fiber Optic Cable

Fiber optic cable is sometimes called wave guide or light guide because it guides the light waves along the length of the cable.Multi mode fiber is used for short cable runs, usually 1.6 mi (approximately 2 km) or less.

Single Mode Fiber Optic Cable

Single mode fibre is used outdoors and for long distances.

Single mode fiber optic cable can operate over much longer distances. Because the fiber only allows one mode of light to propagate, light pulses put on the fiber keep their shape much longer. This allows the light pulses to travel much further without interfering with other pulses. Single mode fibre is recommended for cable runs in excess of 1.6 mi.